Four carriages overturned in the smash late Wednesday, smoke billowing from the wreckage, as bodies were lain out under blankets along the tracks.

The wagons piled into each other and folded up like an accordion. One was ripped apart by the force of the crash, one of its ends pushed up into the air.

Several witnesses spoke of a loud explosion.

The accident happened at 8:42 pm (1842 GMT) Wednesday as the train carrying 218 passengers and four staff was about to enter Santiago de Compostela station in the northwestern region of Galicia.

Rescue workers recovered 73 bodies from the train's wreckage and four more victims died later in hospital, said a spokesman for the Galicia high court, increasing an earlier toll figure.

A total of 143 people were said to have various injuries.

Francisco Otero, 39, who was inside his parents' home just beside the section of the track where the accident happened, said he "heard a huge bang. As if there had been an earthquake."

The train had left Madrid and was heading for the town of Ferrol as the Galicia region was preparing celebrations in honour of its patron saint James.

A witness told radio Cadena Ser that carriages overturned several times on a bend and came to a halt piled up on each other.

Public television TVE said the train may have derailed because it was speeding at the time of the accident but a spokesman for state railway company Renfe said it was too soon to say what caused the accident.

"There is an investigation underway and we have to wait. We will know what the speed is very soon when we consult the train's black box," a Renfe spokesman said.